Right now they are just starting dating so i think like/crush would be a better fit. Maybe not to the level of deep love yet. Having a hard is just a normal chemical body reaction. Some are more sensitive than others=easy to get hard and sometimes that can be seen as pervert.
But at the end of the chapter, seven ask him if he is interested in him, and aisuke is just keeping silence, so seven take it as a yes, but thats weird, cause the manga show us how aisuke think, but he never has think of seven in a romantic way :/
An interest can be a crush, I think what Guilty pleasure said is right. He's feeling an attraction not deep enough to suffer from living together and that's it for now
Need to give the author times for character/relationship development. There will be another volume so this is not the end.
Its just me or it doesnt feel like Aisuke is in love with seven? Just being erect doesnt make me understand the deep of his love heheheh